The present invention combines a centrifugal chiller, used as a compressor/condenser with the electric power generator into a single system, thereby applying a refrigerant liquid/vapor as an evaporative cooling medium for the generator components. This method will provide the inner cooling of the stator winding by liquid refrigerant flowing through the hollow conductors and effective evaporative cooling of the generator core-end regions by expansion of the liquid refrigerant into the critically heated areas.
The use of evaporative cooling in an electrical generator is not a new concept, water has been tried as refrigerant. Prior publications have described the inner evaporative cooling of the stator and rotor conductors with water. Reference: xe2x80x9cThe Cooling of Electric Machines and Cablesxe2x80x9d by Theodore D Koning, 1957, Zuid-Nederlandsche drukkerij N. V. Holland; U.S. Pat. No. 3,189,769, entitled xe2x80x9cDynamoelectric Machine Rotor Coolingxe2x80x9d issued to D. Willyoung.
The invention provides for the use of a low-pressure, low-density centrifugal chiller type refrigerant for cooling of the generator components.
Achieving a high power density in the generator is limited, in a large part, by excessive heating of the critically loaded generator components, such as core-end regions. More effective cooling of the core ends may allow for increasing the unit power rating, thereby resulting in more powerful generators.
The same thermal limitation is imposed on the end portion of the field winding. More effective cooling may also reduce the operating temperature of these components, thereby allowing for a higher field current rating.
Water-cooled stator windings may deteriorate over time due to copper crevice-corrosion. Eliminating the water and substituting it with a non-corrosive refrigerant medium also results in better cooling.
The invention allows for a higher unit power rating of the generator by effecting a radical evaporative cooling to the most critically heated generator components (such as core ends), yet utilizing the well known designxe2x80x94liquid cooled stator winding, gas cooled rotor.
The evaporative cooling of the generator components will be made possible through use of the hollow stator winding conductor as a capillary-and-evaporator, which would allow introduction of the cold vapor discharge to the hot spots of the generatorxe2x80x94the core ends and the field end-winding.
Sub-cooled liquid refrigerant at approximately 70 psig and 45-55xc2x0 C. temperature enters the hollow strands at the sub-cooling temperature through a circular tube supply header. Refrigerant continues flowing through the hollow bar strands which serve as the pressure risers.
Strand window dimensions, refrigerant properties and pressure are selected such, that location of the xe2x80x9cbubble pointxe2x80x9d is near to xc2xe of the core length. Liquid refrigerant, which is fed from the supply headers on both ends of the generator, enters selected hollow strands of each bar from the both ends. Each bar clip is designed for two flowsxe2x80x94in and out. Such an arrangement ensures uniform cooling of all sections of the bar.
Refrigerant begins partially evaporating approximately from xc2xd of the core length and continues to the exit at the end arm. Cold refrigerant vapor at approximately 30xc2x0 C. psig and 5xc2x0 C. temperature exits through the exit header nozzles directed towards the core end. Nozzles can be installed on the small tubes, which would be directed to the particular generator spots of the core, step iron, stator core ventilation ducts, rotor centering ring, etc.
The cooling arrangement for the field winding is the same, so the same generator technology and design can be used. Due to a higher heat absorption the heat load, field winding current can be higher, than with hydrogen gas cooling. Evaporative cooling applies only to the stator winding and core which retain essentially the same design.
Accordingly, the invention provides the following benefits.
New effective cooling will allow for a higher unit power of the generator
Potential for copper winding crevice corrosion will be eliminated
Utilization of the existing liquid cooled winding design and technology
No hydrogen related problems, expenses, explosion danger.